$re = '/(?<=(?<!^https)://)[^/]+/m';
$str = 'https://www.google.com/url?client=internal-element-cse&cx=3c360356&q=https://examplesite1.co.uk/aa-vv--cc-dd-gggg-/&sa=U&ved=2ahUKEwjj1cvJ79PuAhXBHc0KHRgvBLsgQIAhAC&usg=AOvVaw2vIHUiy31YKWs5c41Q
https://www.google.com/url?client=internal-element-cse&cx=3c360356&q=http://www.site2.co.uk/wp-content/uploads/2016/12/research-paper.pdf&sa=U&ved=2ahUKEwiphLKMi80KHcLUCMAQFjAFegQIARAC&usg=AOvVawkm-bXjmxsPxLQ9w3
https://www.google.com/url?client=internal-element-cse&cx=3c360356&q=https://examplesite-3.com/home/en/aaa-bbb/38376&sa=U&ved=2ahUKEwixq4K7qttXEKHTOEClsQFjAAegQIARAB&usg=AOvVaw2ouHhfNNTPV';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php